A brief discussion of the brain is in order.
The brain is made up of white matter and grey matter. At autopsy, you can actually see the difference in color. Grey matter holds the bodies of neurons and where the connections between neurons take place (the synapse). White matter are the axons (or wires of the brain), where the information is actually transported from one part of the brain to another part. These bundles are very important in brain function and can only be measured by Diffuse tensor imaging, a specialized MRI scan which looks at movement of water molecules.